Eg.. Say you are towing heavy loads in mountainous areas and figure you need about 400 hp to accomplish your goals at general road speeds, you could gear an higher rpm engine to do it like a rock crawler or just build the 400 hp at you average rpm you drive at say 2000 rpm so the power is just a throttle press away, So the torque needed to do that is 1050 lbs-ft, then you would need to figure out how much displacement would be needed etc.. probably use diesel and a power adder to cut the displacement down some